1. Field of the Invention
The invention relates to a torque sensor coil and a torque sensor using the torque sensor coil.
2. Description of the Related Art
Magnetostrictive torque sensors are used on a magnetostrictive rotating shaft with magnetic permeability varying according to applied stress, and are configured that variation in magnetic permeability of the rotating shaft when distorted under the applied torque is detected as variation in inductance of a detection coil, thereby detecting torque applied to the rotating shaft.
When torque is applied to the rotating shaft, compressive (or tensile) stress acts in a direction inclined at a predetermined angle (e.g., +45 degrees) relative to an axial direction and tensile (or compressive) stress acts in a direction inclined at a predetermined angle in the opposite direction (e.g., −45 degrees) relative to the axial direction. Therefore, when the torque sensor is configured that variations in magnetic permeability in the directions inclined at, e.g., +45 degrees and −45 degrees relative to the axial direction are respectively detected by two detection coils and a difference in voltage between two ends is measured on the both detection coils by using a bridge circuit, etc., torque applied to the rotating shaft can be detected at high sensitivity.
The detection coils of such magnetostrictive torque sensor are formed by winding insulated wires around a hollow cylindrical bobbin which is formed of a non-magnetic material and is provided coaxially with and at a distance from the rotating shaft. Plural first inclined grooves inclined at +45 degrees relative to the axial direction and plural second inclined grooves inclined at −45 degrees relative to the axial direction are formed on the outer surface of the bobbin. Then, a first detection coil is formed by winding an insulated wire around the bobbin along the first inclined grooves, and a second detection coil is formed by winding another insulated wire around the bobbin along the second inclined grooves. Hereinafter, the bobbin and the detection coils formed by winding the insulated wires around the bobbin are referred to collectively as “a torque sensor coil”.
JP-A-2001-021588 and JP-A-2003-347117 may disclose prior arts related to the present invention.